Dual grey- and drinking water reticulation systems could save SA’s high quality water

Municipalities may soon learn to utilise water of inferior quality for uses such as flushing the toilet in an effort to save drinking water. For example, irrigation in South Africa uses approximately 54% of the total freshwater demand followed by another major user, toilet flushing. Domestic toilet flushing consumes between 50 and 70% of a household’s total drinking water supply.

Grey-water from showers, baths, hand basins, laundry tubs and washing machines can provide a solution to our water scarcity challenges. A joint pilot study, conducted by the Universities of Witwatersrand (WITS), Johannesburg (UJ) and Cape Town (UCT), and funded by the Water Research Commission (WRC), is proving that the use of grey-water can be an effective way of saving our high quality water.

A dual grey- and drinking water reticulation system is a system consisting of separate pipes that supply grey-water (for only toilet flushing in this project) and drinking water, respectively, to the end user. This is the first dual grey- and drinking water reticulation system for high-density urban buildings currently piloted in the School of Civil and Environmental Engineering (Hillman Block) at WITS, collects its grey-water from 13 hand-basins and conveys it to a 200 litre tank.

Prior to the grey-water tank are two 2 mm sieves that collect any solid materials which find their way from the hand-basins. These sieves are cleaned once a week. Prior to the sieves are two chlorinators that disinfect the grey-water to kill any micro-organisms. “The grey-water tank had to be kept small so that water is used immediately” says Dr Adesola Ilemobade, project leader at the WITS School of Civil and Environmental Engineering. The tank has two submersible pumps for directing water to the toilet when the toilet is flushed, using a switch within the toilet cubicle. Necessary measures were also put in place to avoid backflows.

The first phase of the pilot project is currently used to flush one female and one male toilet at the WITS Hillman Block. “If accepted by South African municipalities, the project will be beneficial to many water-scarce communities” says Dr Ilemobade. “At this stage the reuse of black water (sewage) is not considered due to the potentially higher public health risks” he adds.

A survey that was followed by a massive user awareness campaign at WITS, UJ and UCT indicated a high level of optimism amongst staff and students with the installation of a dual grey- anddrinking water reticulation system on their campuses.

Dr Adesola maintains that the unit will offer several advantages including: the reduction in participating households’/institutions’ drinking water bills; in areas without waterborne sewerage, grey-water reuse may improve the performance of septic tanks; grey-water reuse supports the growth in greener water strategies; and water conservation.

“The next installation is in progress at a 16-room unit of the Student Village residence at the University of Johannesburg Kingsway Campus where the collection of grey-water will be extended to showers and baths within the unit” says Dr Ilemobade.

“Municipalities constrained by finance will be better empowered to provide unserved communities with drinking water systems since the costs of the system will be reduced as a result of the reduced demand for drinking water due to grey-water reuse” says Mr Jay Bhagwan, a Director managing the study at the WRC. It will further cause reduced effluent discharges to the environment, leaving streams to their natural flow regime.

For more information

Dr. Adesola A. ILEMOBADE School of Civil and Environmental Eng. University of the Witwatersrand, P Bag 3, WITS 2050 South Africa